1. Field of the Invention
The invention relates to a method and apparatus for fabricating gradient lenses.
2. Description of the Related Art, including Information disclosed under 37 CFR 1.97-1.99
Conventional lens manufacturing involves the grinding of a given material or group of multiple fibers into a desired concave or convex shape, or radially changing the index of refraction of the lens material by doping, differential heat treating, cladding, coating, or alloying in a radially non-uniform way.
U.S. Pat. No. 4,101,302, issued July 18, 1978 to Krohn et al, describes a method of achieving local variation in phototropic properties across the face of a glass lens which contains all the ingredients required to produce phototropic behavior, in which the lens is exposed to a locally variable temperature field in such manner that the temperature of one lens portion exceeds the strain point but not the softening point of the glass, while the temperature of another lens portion is below the strain point, thus causing the development of phototropic behavior in only the one lens portion.
U.S. Pat. No. 4,230,396, issued Oct. 28, 1980 to Olshansky et al, and U.S. Pat. No. 4,406,517, issued Sept. 27, 1983 to Olshansky describe methods of fabricating a gradient index optical filament having a core in which the concentration of dopants is varied as a function of the radial distance form the core center to produce a radially varying index of refraction.
U.S. Pat. No. 4,359,267, issued Nov. 16, 1982 and U.S. Pat. No. 4,405,207 issued Sept. 20, 1983 to Kay describe similar lens forming methods in which a plurality of gradient index fibers are assembled into a lens array of the desired shape, with final finishing being accomplished by grinding the array to its exact finished form.
U.S. Pat. No. 4,358,181, issued Nov. 9, 1982 to Gulati et al, describes a method of making a preform for a high numerical aperture gradient index optical waveguide in which the concentration of a first dopant, GeO.sub.2 is changed radially as the preform is built up in order to produce the desired radial refractive index gradient. The concentration of a second dopant, B.sub.2 O.sub.3, is changed radially to compensate for the radial change of thermal expansion coefficient caused by the varying GeO.sub.2 concentration. The growth of the body is accomplished through a cladding process with the B.sub.2 O.sub.3 added to the cladding layer to make the thermal expansion coefficient of the cladding equal to or greater than the composite thermal expansion coefficient of the core. The magnitude of the residual stress at the inner surface caused by thermal expansion gradients is reduced and premature cracking of the preform is eliminated.
U.S. Pat. No. 4,547,210, issued Oct. 15, 1985 to Schneider, describes a process for drawing gradient optical fibers from a preform that itself is constructed of different composition filaments or tapes that are heated under specific conditions involving oxidizing atmospheres and chlorine gas.
U.S. Pat. No. 4,425,146, issued Jan. 10, 1984 to Izawa et al, describes a method of making a glass caveguide for an optical circuit in which halides of Si and Ti, B, P, or Ge and oxygen or steam are introduced into a reaction vessel and heated in a vapor phase to form fine glass particles by oxidation or hydrolysis. The fine glass particles are depositied on a substrate. They are then heated and vitrified into a transparent glass layer which is etched to form a core having a desired pattern by a reactive sputter etching process using freon gas. The core is coated by a clad. In the waveguide thus formed, the cross-sectional configuration and dimensions of the core layer and the refractive index difference are precisely controlled. An expansion coefficient transient layer is provided between the substate and the core layer to prevent a crack in the waveguide.
U.S. Pat. No. 4,473,273, issued Sept. 25, 1984 to Hodge, describes a method of forming a high bandwidth optical fiber in which the refractive index profile of the fiber is modified by rotating the fiber while drawing the first fiber from a preform. This method involves no deposition process.
U.S. Pat. No. 4,310,340, issued Jan. 12, 1982 to Sarkar, describes a method of making optical fiber waveguides in which a glass optical waveguide preform is prepared by chemical reaction of vapor ingredients in a bait tube. As the reactants flow through the bait tube, a hot zone traverses the tube to cause the deposition of soot in a section of the tube just downstream of the hot zone. An axially disposed tubular burner, which is located just upstream from the hot zone, is mechanically coupled to the burner which generates the hot zone. The burner generates as axial water-free flame that extends through the hot zone. The flame creates a mandrel which confines the flow or reactants to an annular channel adjacent the bait tube wall in the hot zone. The flame also extends downstream from the hot zone where it increases the thermal gradient between the axis and the wall of the bait tube, thereby enhancing the thermophoresis effect, whereby the deposition rate and efficiency are improved.
Chapter 6, pages 225-256, of the book entitled THE GROWTH OF SINGLE CRYSTALS, by R. A. Laudise, copyrighted 1970 by Prentice-Hall, Inc., Englewood Cliffs, N.J., provides a summary of many of the various techniques of vapor-solid growth. There is many publications describing in detail each of these techniques. For example, the CVD process is described in an article entitled "Monolithic material fabrication by chemical vapour deposition", by Goela and Taylor, Journal of Materials Science (1988), pages 4331-4339.